The present invention relates to a method of processing a moving picture, and particularly relates to a picture-processing method of extracting an image of a moving object, which is suitable for a process in which an edge image of a moving object is extracted from a moving picture inputted successively in real time from an image pick-up element moving within a plane perpendicular to an optical axis.
Conventional systems for processing pictures relating to an image of a moving object execute the process by using values obtained from time differentiation or other similar operations with respect to each picture element of a moving picture inputted successively. The time differentiation or similar operations by an electronic circuit can be executed at a very high speed, since this circuit has a simplified construction. It is difficult, however, to extract an image of a moving object only from the values obtained from the time differentiation or similar operations. When a circular area shifts its position before a plain background, for instance, crescent-shaped areas having different signs are outputted in the front and the rear in the shifting direction, and it is hard to extract the circular area from these pieces of information.
There is another method, in this connection, in which images obtained from an image pikk-up element in a conventional manner are stored once in a storage device, pictures are then taken out one by one from the storage device, and the respective corresponding point of each picture is calculated so as to extract an image of a moving object. While the image of a moving object can be extracted correctly according to this method when the corresponding point can be found, since an amount of movement of the object is calculated correctly in this case, a longer time is required for processing said point. It is very difficult, in addition, to detect the corresponding point in the case where there is a rotation, a change in shape or other change of the object.
There is still another known method in which only an image of a background wherein the image of a moving object is not contained is stored beforehand in a device, and images inputted successively are compared with the image of the background so as to extract the image of the moving object. This method can not be applied at all when the image pick-up element is moved or when the background changes. In Japanese Patent Laid-Open No. 8087/1984, a mechanism for renewing an image of a background is contained. By using this mechanism, instantaneous images not containing an image of a moving object are taken successively in a device and stored as a background image therein. This is a contrivance avoid regarding a slow change in time of the background mistakenly as an image of the moving object. According to this method, however, the renewal of the image of the background is not conducted at all when the moving object is present constantly within a pick-up scope, for instance, and it is impossible to cope with a sharp instantaneous change of the background. In addition, this method is also ineffective when the image pick-up element is moved.